International application PCT/AU2004/001421 in the name of the applicant describes an invention of the sulfate process made by the applicant (hereinafter referred to as “the sulfate process of the applicant”). The disclosure in the International application is incorporated herein by cross-reference.
In general terms, the sulfate process of the applicant described and claimed in International application PCT/AU2004/001421 is a sulfate process for producing titania from a titaniferous material (such as an iron-containing titaniferous material such as ilmenite) of the type which includes the steps of:
(a) leaching solid titaniferous material in multiple stages with a leach solution containing sulfuric acid and forming a process solution that includes an acidic solution of titanyl sulfate and iron sulfate;
(b) separating the process solution and a residual solid phase from the leach step (a);
(c) precipitating titanyl sulfate from the process solution from step (b);
(d) separating the precipitated titanyl sulfate from the process solution;
(e) treating the precipitated titanyl sulfate and producing a solution containing titanyl sulfate;
(f) hydrolysing the titanyl sulfate in the solution and forming a solid phase containing hydrated titanium oxides and a liquid phase;
(g) separating the solid phase containing hydrated titanium oxides and the liquid phase; and
(h) calcining the solid phase from step (e) and forming titania.
In addition, the sulfate process of the applicant includes a step of removing iron sulfate from the process solution from step (b) and/or the depleted process solution from step (d) in the form of a slurry of solid iron sulfate crystals and the process solution.
In addition, as is described and claimed in a later-filed International application PCT/AU2007/001320 in the name of the applicant, the sulfate process of the applicant includes a ferric ion reduction step that lowers the concentration of ferric ions in the process solution.
The term “hydrated titanium oxides” is understood herein to include, by way of example, compounds that have the formula TiO2.2H2O and TiO2.H2O.
In addition, the term “hydrated titanium oxides” is understood herein to include compounds that are described in technical literature as titanium hydroxide (Ti(OH)4).
Concentrations of metals mentioned hereinafter are understood herein as being determined by inductively coupled plasma (ICP) (all metals) or by titration (in the cases of Ti and Fe—ferrous and ferric).
The applicant has carried out further research work on the sulfate process of the applicant since the priority date of 17 Oct. 2003 of International application PCT/AU2004/001421 and has identified a number of features that are not disclosed in the International application that are important, separately and in combination, in order to operate the process effectively.
The further research work carried out by the applicant has resulted in the applicant achieving a better understanding of the impact of particulate titanyl sulfate on precipitation of titanyl sulfate from solution during the leach step. In particular, the applicant has found that the presence of particulate titanyl sulfate in the leaching solution during the leach step can act as a seed causing premature precipitation of dissolved titanyl sulfate from solution. The precipitation of particulate titanyl sulfate during the course of the leach step has a far greater adverse impact on the leach step than the applicant thought would be the case and is one of the major factors in preventing the achievement of high extraction rates.
It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.